In double ionization at very high collision velocities Becker has pointed out that so-called direct mechanism obeys the dipole selection rule while the rearrangement mechanism is a monopole transition, and since s and p waves cannot interfere in total cross sections, interference between these mechanisms is forbidden. It is shown here that interference is possible due to dipole-forbidden contributions to the direct mechanism or rearrangement process.

• Received 5 June 1987

DOI:https://doi.org/10.1103/PhysRevA.36.4089